The looming
U.S. Navy attempt to shoot down a dying satellite could demonstrate an
anti-satellite capability for its missile defense system.

A
successful kill would mark the first time the United States uses a tactical missile to destroy a spacecraft  assuming
that the ship-based missile defense system can handle the high closing speed of
more than 22,000 mph.

"Everything
becomes much more stressful at these large closing speeds," said Geoffrey Forden,
MIT physicist and space expert. "But if they do hit it, that'd be very
impressive, and that'd be proof that it has ASAT [anti-satellite]
capability."

How it
would work

The Navy looks
to rely on its Aegis Ballistic Missile Defense System based on U.S. cruisers and destroyers, which was developed to
protect U.S. forces and allies against short-
and medium-range ballistic missiles. The interceptors rely on kinetic energy
from their combined mass and speed to smash into their targets.

Three naval
ships stand ready in the North
Pacific Ocean to each take a
shot with a modified Standard Missile-3 (SM-3). If the first attempt
misses, the other two ships can take turns as backups.

The
modified SM-3 interceptors will supposedly be able to identify the falling U.S. spy satellite based on changes in their targeting
software. However, Forden expressed caution as to whether the Aegis system can
score a successful satellite kill at such high closing speeds  previous tests
involved much slower-moving targets.

"I'll
be very surprised if it works," Forden said, pegging the chances at
"less than 50-50."

The United States has managed to take out satellites
with other weapon systems in the past. An F-15
Eagle fired a missile-launched kill vehicle that struck and destroyed a
target satellite in 1985. SPACE.com's Leonard David also noted a 1986 "Star
Wars" test by the Strategic Defense Initiative Organization involving
the first space-to-space intercept of a target.

Not
alone

The United States is not alone in its anti-satellite
tests. China used a missile to shoot down an
old weather satellite a year ago, leaving a cloud of debris that will
present a low-risk threat to other satellites and space missions for up to 20
years.

A U.S. intercept of its falling spy satellite would happen
low enough to avoid debris endangering the International Space Station, and
would only occur after space shuttle Atlantis has safely landed.

Success for
the United States would boost the perceived capabilities
of the Aegis system, but could also heighten international concern over U.S. missile defense systems being used to target
satellites.

"All
along, other countries have said missile defense has offensive capabilities,
and in fact is better suited for such," noted Joan Johnson-Freese, NavalWarCollege security expert, in an e-mail to
SPACE.com. "While the U.S. has
ignored/downplayed those concerns, this test will basically prove that those
concerns were valid."

Senior U.S. officials apparently tried to allay such concerns at
the Feb. 14 press briefing by emphasizing that the missile modifications would
be difficult to make on a fleet-wide basis.

Concerns
remain

Yet
Johnson-Freese also observed that the U.S. Navy's three potential attempts
"equates to lots of target practice  without international
condemnation," because the U.S.
has declared the falling satellite a threat to public safety. That still has
not prevented China and Russia from expressing
their concerns.

Forden
pointed out that the U.S. interception attempt could also
help legitimize the earlier Chinese anti-satellite test which was heavily
criticized by the U.S. and other countries. Setting a
precedent now could open the door for future anti-satellite tests by other
countries, added Johnson-Freese.

A slight chance
also exists that China might be tempted to test its proven
anti-satellite capability again, should the U.S.
attempts fail to destroy the falling satellite.

"China has said it would take preventive
measures, and that's the only thing that makes sense," Forden said.